Fill blood collection tubes completely (until vacuum is exhausted) to ensure the correct blood to anticoagulant ratio necessary for accurate patient results. Specimens may be rejected by the laboratory if the tube is short-filled or over-filled.

To avoid short-filling of tubes, the phlebotomist must ensure that the blood flow stops completely before removing the tube from the needle.

When using a winged device (butterfly) to collect blood for coagulation studies (e.g., protime, aPTT), the phlebotomist must draw a "waste" tube before attaching another light blue top tube for testing. This waste tube must be a tube without additive or another light blue top tube. If the air in the tubing of the winged device is not displaced into a waste tube and is drawn into the tube used for testing, the tube used for testing will short-fill. The laboratory may reject the specimen because of invalid blood to anticoagulant ratio.